Sol-gel derived sensor for rapid determination of heavy metals

Abstract

The present application is directed to a novel approach for rapid, selective and sensitive detection of heavy metals using a solid-phase bioactive lab-on-paper sensor that is ink-jet printed with sol-gel entrapped reagents to allow colorimetric visualization of the enzymatic activity. The bioactive paper assay is able to detect a range of heavy metals, either alone or as mixtures, in as little as 10 min. The paper-based assay was immune to interferences from non-toxic metal ions such as Na + or K + , could be used to detect heavy metals that were spiked into tap water or lake water, and provided quantitative data that was in agreement with values obtained by atomic absorption. The paper-based sensor is of value for rapid, on-site screening of trace levels of heavy metals in resource limited areas and developing countries.

1 . A sensor for detecting heavy metals comprising:
 (a) an enzyme entrapped within a sol gel material immobilized in one or more sensing zones on a paper substrate; and   (b) a substrate for the enzyme comprised within a sol gel material immobilized on one or more substrate zones on the paper substrate;   wherein the one or more sensing zones are located relative to the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of an eluent across the paper substrate in a direction from the one or more substrate zones to the one or more sensing zones, and   the enzyme's activity is inhibited by heavy metals.   
     
     
         2 . The sensor of  claim 1 , wherein the enzyme is β-galactosidase (B-GAL). 
     
     
         3 . The sensor of  claim 1 , wherein the heavy metal is selected from Zn(II), Cu(II), Cd(II), Pb(II), Ag(I), Cr(VI), Ni(II) and Hg(II). 
     
     
         4 . The sensor of  claim 1 , further comprising a hydrophobic barrier located relative to the one or more sensing zones such that leaching of the enzyme and/or substrate from the one or more sensing zones is inhibited. 
     
     
         5 . The sensor of  claim 1 , wherein inhibition of the enzyme's activity is detected using one or more of fluorescence, colorimetry, ultra violet spectroscopy and infrared spectroscopy. 
     
     
         6 . The sensor of  claim 5 , wherein inhibition of the enzyme's activity is detected using colorimetry. 
     
     
         7 . The sensor of  claim 1 , wherein the sol gel material is a silica material. 
     
     
         8 . The sensor of  claim 1 , wherein the sol gel material is deposited on the paper substrate using ink-jet printing of a silica precursor material. 
     
     
         9 . The sensor of  claim 1 , wherein the one or more sensing zones are located above the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of an eluent up the paper substrate. 
     
     
         10 . The sensor of  claim 1 , wherein the one or more sensing zones surround the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of an eluent in a concentric fashion out from the one or more substrate zones. 
     
     
         11 . A method to detect presence of heavy metals in a sample using a sensor comprising:
 a) an enzyme entrapped within a sol gel material immobilized in one or more sensing zones on a paper substrate; and   b) a substrate for the enzyme comprised within a sol gel material immobilized on one or more substrate zones on the paper substrate;   wherein the one or more sensing zones are located relative to the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of an eluent across the paper substrate in a direction from the one or more substrate zones to the one or more sensing zones, and   the enzyme's activity is inhibited by heavy metals,   the method comprising:   i) contacting the sample with the one or more sensing zones;   ii) placing an eluent at a location proximal to the one or more substrate zones such that the eluent travels by lateral flow across the paper substrate, passing first through the one or more substrate zones and then through the one or more sensing zones; and   iii) monitoring the one or more sensing zones for a detectable change,   wherein a detectable change in the one or more sensing zones in the presence of the sample compared to a control indicates the presence of heavy metals in the sample.   
     
     
         12 . The method of  claim 11 , wherein the enzyme is β-galactosidase (B-GAL). 
     
     
         13 . The method of  claim 11 , wherein the heavy metal is selected from Zn(II), Cu(II), Cd(II), Pb(II), Ag(I), Cr(VI), Ni(II) and Hg(II). 
     
     
         14 . The method of  claim 11 , wherein the sensor further comprises a hydrophobic barrier located relative to the one or more sensing zones such that leaching of the enzyme and/or substrate from the one or more sensing zones is inhibited. 
     
     
         15 . The method of  claim 11 , wherein inhibition of the enzyme's activity is detected using one or more of fluorescence, colorimetry, ultra violet spectroscopy and infrared spectroscopy. 
     
     
         16 . The method of  claim 15 , wherein inhibition of the enzyme's activity is detected using colorimetry. 
     
     
         17 . The method of  claim 15 , wherein the sol gel material is a silica material. 
     
     
         18 . The method of  claim 15 , wherein the sol gel material is deposited on the paper substrate using ink-jet printing of a silica precursor material. 
     
     
         19 . The method of  claim 11 , wherein the one or more sensing zones are located above the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of the eluent up the paper substrate. 
     
     
         20 . The method of  claim 11 , wherein the one or more sensing zones surround the one or more substrate zones such that the substrate moves from the one or more substrate zones into the one or more sensing zones by lateral flow of the eluent in a concentric fashion out from the one or more substrate zones.